1. Field of the Invention
The present invention relates to a process for the isolation and removal of benzene from a fluid catalytically cracked naphtha. More particularly the invention relates to a process wherein benzene is first concentrated in a C6 fraction and the C6 fraction subjected to etherification to preserve the isoolefins during subsequent benzene removal steps.
2. Related Information
Benzene, while being a useful commodity chemical, is a toxic component of gasoline. Consequently many countries have laws that limit its concentration in gasoline to about one percent. To meet these current limits some refiners need to produce reformate which is low in benzene content. This can be done by removing benzene precursors from the reformer feed or by hydrogenation of the benzene in the reformer product. Another method is to remove the benzene by solvent extraction. However, if benzene limits continue to be reduced, the benzene in the fluid catalytically cracked (FCC) naphtha may need to be removed. Catalytically cracked naphtha gasoline boiling range material currently forms a significant part (≈⅓) of the gasoline product pool in the United States and it contains about 1.5% benzene.
Removing benzene from FCC naphtha streams is difficult because the benzene is accompanied by many close boiling olefins and sulfur compounds. A benzene rich fraction may be isolated by fractionation. Extraction of benzene from either a concentrate or the full naphtha stream would require complete saturation of the olefins present (i.e., a Bromine Index of less than 500) which would be very detrimental to the octane of the naphtha. An alternative to extraction would be hydrogenating the benzene in either the full stream or a benzene concentrate. If a full boiling range FCC naphtha were subjected to this treatment, the hydrogen consumption and the octane loss would be extremely high. Ideally only the C6 fraction would be subject to this treatment. However, even treating this fraction would result in high hydrogen consumption and loss of octane.
In addition to benzene, sulfur must be lowered to meet stricter limitations. Hydrogenating organic sulfur compounds to only about 0.1 wppm sulfur, is similarly detrimental to the olefins.
The present invention addresses all of these concerns by removing benzene and sulfur while preserving the octane component of the olefins.